1. Field of the Invention
The present invention relates to the field of electronic surge protection circuits. More specifically, the invention relates to a surge protection circuit for communication networks that carry high-speed digital signals.
2. Description of the Related Art
In a typical communication network, telephone lines carry voice and data signals from a remote unit to a local unit. For example, in the context of a digital loop carrier (xe2x80x9cDLCxe2x80x9d) system for extending fiber optic cable into the local-loop between a central office location and a plurality of subscribers, the remote unit could be a remote digital terminal (xe2x80x9cRDTxe2x80x9d) or an optical network unit (xe2x80x9cONUxe2x80x9d), and the local unit could be a network interface device (xe2x80x9cNIDxe2x80x9d). The NID further couples the signals to the subscriber""s telephony and data devices, which are referred to as customer premises equipment (xe2x80x9cCPExe2x80x9d).
The connections between the local units and the CPE usually include unshielded twisted pair (xe2x80x9cUTPxe2x80x9d) wire. There is a first twisted pair used for incoming signals that travel from the network towards the CPE and a second twisted pair used for outgoing signals that travel away from the CPE towards the network. These UTP wires are susceptible to voltage and current surges often caused by lightning strikes or AC power (60 Hz) crosses. Therefore, surge protection devices or circuits are typically coupled to the UTP wires to protect the remote and local units, and the CPE, from being damaged by over-voltage and over-current conditions. For signal lines that carry high speed signals, such as 10Base-T Ethernet signals, such surge protection devices must have a low insertion-loss in order to avoid attenuation of the signals at high frequencies.
A communications system including an over-voltage and over-current surge protection circuit is provided that passes high frequency signals between transmitting and receiving devices with low attenuation. The protection circuit includes a current limiter and over-voltage protection device. The over-voltage protection device includes a diode device comprising a set of anti-parallel diodes, which is connected in series with a shunt device. The over-voltage protection device is coupled between a signal transmission line and ground. The current limiter is coupled between the transmitting and receiving devices.
As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description of the preferred embodiments are to regarded as illustrative in nature and not restrictive.